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20121104
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, sampling and testing its water for signs of pollution. because of sandy soils and the soluble limestone-bedrock geology in this part of florida, rivers here run above ground and then flow underground through sinkholes. above ground, water can be sampled directly. but underground, the water fills and moves through the porous rock aquifer. this water can be accessed through a series of wells. the aquifer water here, the water that's contained in the rocks in the very small, microscopic, pore spaces within the rock, is what's utilized for drinking water and, actually, allater, so agriculture-irrigation water, bottling water, any kind of water usage is almost all from ground water. narrator: by carefully measuring the depth of ground water, main's team can calculate how much is being used. 17.29. they also record the water's chemical composition to determine nutrient levels that could adversely affect the health of the water. okay, we're ready to sample. narrator: one key nutrient they sample for is nitrate. actually, nitrate is regulated in drinking water standards by the environmental pro
downstream. if you've ever waded across a river and felt the sandy bottom moving beneath your feet, you've experienced hydraulic action. the faster the river flows, the greater the turbulence, and the swirling flow of a very rapid stream can even wrench chunks of fractured bedrock off of the channel bottom. the rapid current of a sediment-laden river can also generate a sand-blasting effect which can scour its way down through sediment or even solid rock. in this process, called abrasion, the energy of the moving water is converted into collisions between sedimentary grains and the bedrock of the channel bottom. abrasion not only smooths river cobbles into rounded shapes, it can also wear away the bedrock many times faster than hydraulic action alone. running water also, to some degree, dissolves any type of rock or mineral. this process of erosion, called dissolution, is controlled in part by the mineral composition of the bedrock. for example, a river bed made of limestone will dissolve more rapidly than one made of granite. the rate of erosion by dissolution is also controlled by tem
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